1. (BIOC 231) Enzyme Kinetics
Dr. Ayat B. Al-Ghafari

2. Learning Objectives
By the end of the lecture, the student should be able to :
Define Enzyme kinetics
Describe the several types of reaction order
Know the Michaelis-Menten equation
Explain the several modification models for M-M equation

3. Enzyme Kinetics
Study of reaction rate and how they changes in response to change in experimental parameter is known as kinetics
Amount of substrate present is one of the key factor affecting the rate of reaction catalyzed by an enzyme in vitro

4. Low of Mass Action

5. Zero Order Reaction
The rate is independent of the concentration of any of the reactants

6. First Order Reaction

7. Second Order Reaction

9. Michaelis-Menten Kinetics
The quantitative theory of enzyme kinetics was proposed by two scientists Leonor Michaelis and Maud Leonora Menten in 1913
Enzyme reactions in Michaelis–Menten kinetics theory occur in two stages:
The substrate binds reversibly to the enzyme, forming the enzyme-substrate complex. This is sometimes called the Michaelis-Menten complex
The enzyme then catalyzes the chemical step in the reaction and releases the product (Briggs & Haldane)

10. Kinetics of single-substrate enzyme-catalyzed reactions
The relationship between initial velocity and substrate concentration was first suggested by Michaelis-Menten in 1913
The general equation is:
k1 k2
E + S ES E + P
k-1
Where,
S is the substrate
E is the enzyme
K1, k-1 and k2 are the rate constants

14. Effect of Substrate Concentration on Reaction Velocity

15. The Briggs- Haldane modification of M-M equation
Briggs & Haldane introduced a more generally valid assumption in 1925
Steady-State assumption: [ES] and [E] are low compared to [S]
Then, the rate of change of [ES] would be negligible compared to the rate of change of [P] over initial reaction period
Once ES complex is formed, it is maintained at steady state: ES would be broken down as fast as it is being formed
k k2
E + S ES E + P
k-1

18. Lineweaver-Burk (double reciprocal) plot
A linear representation is more accurate and convenient for determining Vmax and Km
This equation is obtained by taking reciprocal of both the side of Michelis-Menton equation (or Briggs- Haldane modification)
1/[S] vs. 1/Vo

19. Lineweaver-Burk (double reciprocal) plot

20. Lineweaver-Burk (Double Reciprocal) Plot

21. What does enzyme kinetic mean?
Enzyme rates depend on two major factors:
Solution conditions
Substrate concentration
To find the maximum speed of an enzymatic reaction, the substrate concentration is increased until a constant rate of product formation is seen (saturation curve)
Saturation happens because, as substrate concentration increases, more and more of the free enzyme is converted into the substrate-bound ES complex

22. SATURATION CURVE

23. What does enzyme kinetic mean?
At the maximum reaction rate (Vmax) of the enzyme, all the enzyme active sites are bound to substrate, and the amount of ES complex is the same as the total amount of enzyme
There are other several important kinetic parameters
The Michaelis-Menten constant (Km), which is the substrate concentration required for an enzyme to reach one-half its maximum reaction rate
Each enzyme has a characteristic Km for a given substrate

24. What does enzyme kinetic mean?
kcat, also called the turnover number, which is the maximum number of substrate molecules which can be converted to products per molecule of enzyme per unit time (usually in seconds)
The efficiency of an enzyme (the specificity constant) can be expressed in terms of kcat/Km

25. References
Harvey, R., and Ferrier, D. (2011) Lippincott’s Illustrated Reviews: Biochemistry 5th edition.
Murray, R. et al., (2012) Harper’s Illustrated Biochemistry 29th edition.